Adds Terrascan pre-commit (#953)

Adds pre-commit integration for Terrascan

Co-authored-by: mihirhasan <[email protected]>

.pre-commit-hooks.yaml

@@ -0,0 +1,5 @@
+- id: terraform-pre-commit   
+  name: terrascan
+  description: Runs terrascan on supported IaC templates.
+  language: script
+  entry: scripts/pre-commit-hook.sh  

docs/integrations/pre-commit-integration.md

@@ -0,0 +1,63 @@
+# Integrating Terrascan with Pre-commit 
+
+## Overview 
+Terrascan scan can be used as a pre-commit hook in order to automatically scan your IaC before every commit. 
+For more information about pre-commit hooks see https://pre-commit.com/#intro 
+
+___
+
+**Requirements**
+
+* Ensure Terrascan is properly installed  (See https://runterrascan.io/docs/getting-started/#installing-terrascan)
+* Have Pre-commit package manager installed (See https://pre-commit.com/#install)
+___
+## Integration Method 
+___
+### Add config file 
+1. Add file called .pre-commit-config.yaml to root of repo you wish to scan with pre-commit. It should look like this: 
+```yaml
+repos:
+    - repo: https://github.com/accurics/terrascan
+        rev: <COMMIT/VERSION>  
+        hooks:
+        - id: terraform-pre-commit
+            args: [ '-i <IAC PROVIDER>'] #optional 
+```
+**Note:**
+The optional args line allows you to specify the IaC provider. For example, 
+```yaml
+repos:
+    - repo: https://github.com/accurics/terrascan
+        rev: <COMMIT/VERSION>  
+        hooks:
+        - id: terraform-pre-commit
+            args: [ '-i k8s'] 
+```
+will cause 
+```bash
+'terrascan scan -i k8s' 
+```
+to run and thus scan kubernetes yaml files. You may exclude the args like so: 
+```yaml
+repos:
+    - repo: https://github.com/accurics/terrascan
+        rev: <COMMIT/VERSION>  
+        hooks:
+        - id: terraform-pre-commit
+```
+which causes the default 
+```bash
+'terrascan scan' 
+```
+to be run, scanning all IaC provider types. 
+
+___
+
+Once you have everything installed, and add the appropriate config file to your repo, 
+```bash
+'terrascan scan -i <IAC PROVIDER>' 
+```
+everytime you attempt to commit your staged changes. You can also call the hook directly on all files using pre-commit run --all-files 
+
+
+